Outdoor barbeque grills used for cooking food are typically fired with one of three conventional heating systems. The heating systems are typically either charcoal briquettes in a smoldering condition, burners fueled with either natural gas, propane, or a similar fuel, or by means of electrical elements that may be used alone or in conjunction with a heatable radiant material. Over the years, the use of heatable radiant materials has evolved from charcoal briquettes to lava rocks, to ceramic briquettes, plates or blocks. Such a construction is shown by U.S. Pat. No. 3,277,948 or 3,561,902, to Best. Other types of radiant burners use woven ceramic mesh, woven metal wire, and perforated metal plates as described in various patents over the years. However, with the advent of new burners, emissions standards, and, of course, the safety concerns that surround outdoor cooking, the field has continued to evolve.
In conjunction with the infrared emitting apparatus, described in U.S. Patent Publication No. 2006/0002157, a radiant infrared burner is shown for use in heating a ceramic glass emitter. However, radiant infrared burners of known type of construction have various limitations including limited gas flow turn down ratio (defined as the ratio of the maximum gas flow to the minimum possible gas flow), a propensity to extinguish under windy conditions, radiant transfer of heat in a direction downward into the surrounding plenum chamber, high pressure drop across the radiant element, and high cost of fabrication. Also some radiant burners depend on mostly primary air for combustion. That is, all the air required for combustion of the gas is mixed with the gas prior to admission to the burner body. Therefore, the inlet gas-air mixture is ready for ignition and so the auto ignition point due to ambient temperature is relatively low which can cause internal fires in the burner. In addition, radiant burners have surfaces that are at temperatures of 1600 to 1800 degrees F. which are challenging to all types of materials in terms of longevity due to thermal cycles or thermal shock in the case of ceramics or high temperature corrosion in the case of metals.
Best, in US 2009/0202688, addresses many of these concerns by disclosing a method and apparatus for generating infrared radiation from convective products of combustion. Best teaches the construction of a large box underneath an appropriate infrared re-emitter in which various types of burners are shown mixing products of combustion and distributing them under the re-emitter. Various types of re-emitters are described including solid plates that route all products of combustion around the food cooking area and surfaces that have some openings in them to allow some or all products of combustion to pass through the surface into the food cooking area. In some embodiments the use of internal baffles is shown to further convert convective to radiant heat while in other embodiments these baffles are absent. In all cases the admission of secondary combustion air to the burner is substantially remote to the burner ports and the depth of the box is considerable to allow complete and uniform mixing to evenly heat the re-emitter. In some cases the high temperatures inside the box require the use of a special complex burner construction to avoid the phenomenon of pre-ignition of the primary air-gas mixture. An improvement will be shown that allows construction of a device generating infrared radiation from convective products of combustion with a much smaller depth and avoiding completely the problem of pre-ignition by employing a novel method of using secondary air required for combustion as cooling for the burner tubes.